Distance in an eye is one of important parameters for ophthalmologic diagnosis. For example, axial length that indicates distance between a cornea and retina is used in diagnosis of axial myopia and axial hypermetropia. Further, locations (relative locations with respect to a characteristic site of the eye, for example) and sizes (distance from one end to the other end, for example) of lesions are also important information for making diagnostic decision. Hereinafter, such a distance in an eye is sometimes referred to as an “intraocular distance”. Known methods of measuring intraocular distances include methods using ultrasounds and methods using optical coherence tomography (OCT).